Strength and heat resistance are required in heat-resistant protective suits such as fire-fighting clothing and clothing used in disaster relief, and usually para-aramid fibers are used therefor. However, para-aramid fibers are problematic in that they have poor light resistance and undergo photodegradation when exposed to sunlight, exhibiting an immediate loss of strength and suffering discoloration. Therefore, blending with a meta-aramid fiber or the like has been proposed for securing light resistance (Patent Document 1).
However, even when a para-aramid fiber and a meta-aramid fiber are blended as proposed in Patent Document 1, the problems that the para-aramid fiber present on the surface undergoes photodegradation when exposed to sunlight, immediately loses strength, and experiences discoloration still remain. In the case of a blended yarn in particular, since respective fibers that constitute the spun yarn are moved outward and inward within the yarn due to the phenomenon called migration, degradation that has occurred in exposed portions results in deterioration in the strength of the entire yarn. Moreover, an ordinary multilayer-structured spun yarn is also problematic in that the core fiber and the cover fiber separate and a high-tenacity yarn is not likely to be obtained.    Patent Document 1: JP 2007-077537A